title: A computational study of the mechanism of hydrogen evolution by cobalt(diimine-dioxime) catalysts.
abstract: Cobalt(diimine-dioxime) complexes catalyze hydrogen evolution with low overpotentials and remarkable stability. In this study, DFT calculations were used to investigate their catalytic mechanism, to demonstrate that the initial active state was a Co(I) complex and that H2 was evolved in a heterolytic manner through the protonation of a Co(II)-hydride intermediate. In addition, these catalysts were shown to adjust their electrocatalytic potential for hydrogen evolution to the pH value of the solution and such a property was assigned to the presence of a H(+)-exchange site on the oxime bridge. It was possible to establish that protonation of the bridge was directly involved in the H2-evolution mechanism through proton-coupled electron-transfer steps. A consistent mechanistic scheme is proposed that fits the experimentally determined electrocatalytic and electrochemical potentials of cobalt(diimine-dioxime) complexes and reproduces the observed positive shift of the electrocatalytic potential with increasing acidity of the proton source.
authors.affiliation: Dynamo Team, DYNAMOP Group, UMR 5075, Université Grenoble 1, CNRS, CEA, Institut de Biologie Structurale "Jean-Pierre Ebel", 41 rue Jules Horowitz, 38027 Grenoble Cedex 1 (France).
authors.forename: Anirban
authors.initials: A
authors.lastname: Bhattacharjee
authors.forename: Eugen S
authors.initials: ES
authors.lastname: Andreiadis
authors.forename: Murielle
authors.initials: M
authors.lastname: Chavarot-Kerlidou
authors.forename: Marc
authors.initials: M
authors.lastname: Fontecave
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Field
authors.forename: Vincent
authors.initials: V
authors.lastname: Artero
mesh_terms: D002384:Catalysis; D003035:Cobalt / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry*; D008024:Ligands; D011522:Protons
chemical_list: D008024:Ligands; D011522:Protons; D003035:Cobalt; D006859:Hydrogen
keywords: bridging ligands; cobalt; density functional calculations; hydrogen evolution; proton coupled electron transfer